Since the first practical demonstration of photovoltaic (PV) cells, devices used to convert sunlight directly into electrical energy, was performed in 1954, people have sought to employ the technology for terrestrial energy production on an ever-increasing scale. To enable this and other solar technologies, such as solar thermal and solar thermal-electric systems, to perform optimally, evaluation methods and processes have been developed by scientists and researchers to map the relative concentration of solar radiation hitting the earth's surface in different geographic locations. This process of mapping the sun's intensity is generally referred to as solar resource assessment. Traditional solar resource assessment can, in many ways, be likened to prospecting, albeit with the use of sophisticated instruments and highly rigorous scientific methods and practices. Some of the products of this assessment process are databases that catalog the regional intensity of the solar resource, on an hourly basis, over the course of many years. These databases are often displayed as maps with topographic-like demarcation and shadings corresponding to the intensity of the average annual solar resource. Because the solar radiation hitting the earth's surface is highly dependant upon the local meteorological conditions it can vary from one day, week, month or year to the next. Therefore, the databases usually contain time periods large enough (perhaps as much as thirty years) to smooth the year-to-year variation and approximate the characteristic annual climate conditions of the site being assessed. A single representative year of assessment data for a site can be synthesized from an average of a larger multi-year database. One method used to create such a representative year is to select the most “typical” individual months from a database of thirty years, and combine them to form a typical meteorological year (TMY). The resulting one-year database of irradiance and weather data is predictive of the conditions that can be expected for a site over a period similar to the original sampling period of thirty years.
Once these solar resource databases are compiled they can be used as inputs into software programs that simulate electrical energy production from solar generating systems. These simulation programs use the solar resource data for a given location, in combination with the physical parameters of a particular solar generating system, —such as system size, orientation angles, equipment types, electrical characteristics, shading obstructions, latitude, longitude, elevation, and other features, needed to characterize the solar generator—to estimate the useful energy that can be expected from the system over the course of a period of time comparable to the original data-sampling period. Using such a process, it is possible to estimate the useful energy that would be produced by a solar generating system over its thirty-year lifetime.
Presently, solar energy contributes only a tiny fraction of the electrical energy consumed within the electrical grid. In its present form, the electrical grid, both in its physical structure and in its market configuration, is not designed to incorporate a significant percentage of its daily energy transactions from solar energy. Because, with present technology, large amounts of electrical energy cannot be stored cost effectively, the grid requires constant management to balance production with demand. Electricity is a product that must be used as soon as it is produced. Because it is so essential and critical to our society, reliability standards are extremely high, often referred to as being in the “high nines.” This standard indicates that it is expected that service will be present and within specifications 99.999% of the time. For the engineers who must manage the dispatch of generation, the reserves and the transmission constraints of the grid, grid-tied solar energy presents no problem as long as its contribution is a small percentage of the energy flowing through the system. For traders in deregulated wholesale energy markets who resell energy to end users, and who must anticipate their customer's demand, solar energy generation that is distributed amongst those customers, presents no problem, again, so long as that generation makes up only a small percentage of the total demand.